The field of free-form fabrication has seen many important recent advances in the fabrication of articles directly from computer controlled databases. These advances, many of which are in the field of rapid manufacturing of articles such as prototype parts and mold dies, have greatly reduced the time and expense required to fabricate articles. This is in contrast to conventional machining processes in which a block of material, such as a metal, is machined according to engineering drawings.
Examples of modern rapid manufacturing technologies include additive layer manufacturing techniques such as electron beam melting, selective laser sintering (SLS), selective laser melting (SLM), and other three-dimensional (3-D) processes. When employing these technologies, articles are produced in layer-wise fashion from a laser-fusible powder that is dispensed one layer at a time. The powder is sintered in the case of SLS technology and melted in the case of SLM technology, by the application of laser energy that is directed in raster-scan fashion to portions of the powder layer corresponding to a cross section of the article. After the sintering or melting of the powder on one particular layer, an additional layer of powder is dispensed, and the process repeated, with sintering or melting taking place between the current layer and the previously laid layers until the article is complete. Detailed descriptions of the SLS technology may be found in U.S. Pat. Nos. 4,863,538, 5,017,753, 5,076,869, and 4,944,817, the entire disclosures of which are incorporated by reference herein. Similarly, a detailed description of the use of SLM technology may be found in U.S. Pat. No. 7,537,664 (“the '664 Patent”), the disclosure of which is incorporated by reference herein. The SLM and SLS technologies have enabled the direct manufacture of solid or porous three-dimensional articles of high resolution and dimensional accuracy from a variety of materials including wax, metal and metal alloys, metal powders with binders, polycarbonate, nylon, other plastics and composite materials, such as polymer-coated metals and ceramics.
Other non-powder based additive manufacturing technologies are also known to produce high resolution and dimensionally accurate articles. For example, in fused filament fabrication (FFF) or Plastic Jet Printing (PJP), strands of molten material are extruded from a nozzle to form layers onto a substrate in which the material hardens upon extrusion. Using digital light processing (DLP), photosensitive resin plastic is cured by light and built layer by layer from the bottom-up or a vat of liquid polymer is exposed to balanced levels of ultraviolet light and oxygen to produce a part often from the top-down. In inkjet 3D printing, a liquid binding material is selectively deposited across a thin layer of a powder and the process is repeated in which each new layer is adhered to the previous layer.
The invention claimed in the '664 Patent is one of several commonly owned by Howmedica Osteonics Corporation that relate to the additive manufacturing area. For instance, U.S. Pat. Appl. Publ. Nos. 2006/0147332 A1 (“the '332 Publication”) U.S. Pat. Appl. Publ. No. 2011/0014081 A1 (“the '081 Publication”), U.S. Pat. No. 8,992,703 (“the '703 Patent”), U.S. Pat. No. 9,135,374 (“the '374 Patent”), and U.S. Pat. No. 9,180,010 (“the '010 Patent”), the entire disclosures of which are hereby incorporated by reference herein, have taught the generation and organization of a population of porous geometry, a mathematical representation of the portion of geometry of the porous structure to be built within a region defined by a predetermined unit cell or imaginary volume, to fill and form a predetermined build geometry, i.e., a model build structure, which may be used to produce a near net-shape of an intended porous tissue in-growth structure. The predetermined build geometry, or overall computer-aided design (CAD) geometry, may refer to the mathematical or pictorial representation (such as that on a computer display) of the intended physical structure to be manufactured. In the case of physical components that include both porous material and solid material, the predetermined build geometry may be an assembly of solid and porous CAD volumes that define the outer boundaries of the respective solid and porous materials intended to be manufactured. Furthermore, these applications teach the randomization of the position of interconnected nodes, or points of intersection between two struts or between a strut and a substrate, that define each of the porous geometries while maintaining the interconnectivity between the nodes. As further taught in these applications, such randomization may be accomplished by changing the coordinate positions of the nodes, in the x, y, and z directions of a Cartesian coordinate system, to new positions based on a defined mathematical function.
During surgical operations on one or more bones, orthopedic implants are generally adhered to a bony surface by bone cement. Even proper preparation of delivery of bone cement to a smooth bony surface can result in aseptic loosening of the implant and cement over time, especially when filling large void spaces such as in the proximal tibia and distal femur, requiring a revision surgery to be performed. Current implants, which typically require the use of biocompatible materials such as titanium, used to retain bone cement lack flexibility and are difficult to shape for a proper fit in a non-uniform space. Such implants are non-porous and thus lack limited surface area for contact with bone. Implants produced using additive layer manufacturing techniques have been built with strong scaffolds, but such implants are too rigid to allow for adequate deformation to fill void spaces created by bone degradation.
Thus, a new method is needed to create flexible structures which still provide mechanical strength to resist tensile and compressive forces, especially impact forces applied to bone and orthopedic implants.